Some types of field effect transistors (FETs) have three-dimensional, non-planar configurations including fin-like structures extending above substrates. Such field effect transistors are referred to as FinFETs. The substrates may include semiconductor on insulator (SOI) substrates or bulk semiconductor substrates. Silicon fins are formed in some FinFETs on substrates via known technology such as sidewall image transfer (SIT). FinFET structures including SOI substrates can be formed, in part, by selectively etching the crystalline silicon layers down to the oxide or other insulating layers thereof following photolithography. Active fin heights are set by SOI thickness when employing SOI substrates. In bulk FinFETs, active fin height is set by oxide thickness and etched fin height. At least the bottom portions of the fins of bulk FinFETs should be doped to avoid source-to-drain leakage below the gate. The gates of FinFETs can be formed using a “gate-first” process wherein a gate stack and spacers are formed prior to selective epitaxial growth wherein source and drain regions are enlarged. A “gate-last” process may alternatively be employed wherein the source/drain regions are formed immediately following fin patterning. Gate-last procedures can involve making a dummy gate, fabricating other elements of the transistor, removing the dummy gate, and replacing the removed dummy gate with actual gate materials.
Doped semiconductor material such as silicon or silicon germanium (SiGe) may be provided by selective epitaxial growth on the sidewalls of the fin structure(s) during fabrication of FinFETs. Such growth results in faceted structures that, in some cases, merge into a continuous volume. The faceted epitaxy grown from the fins increases the volumes of the source/drain regions. Such epitaxial growth proceeds from the fins to self-limited, diamond-shaped volumes Problems associated with such structures include managing the merging of neighboring epitaxy. For example, in some locations neighboring epitaxy grown from respective fins may merge. In other locations, neighboring epitaxy grown from respective fins may not merge. Those area with epitaxy merging first creates faster growth facet over other area. This uniformity of growth may cause defects and affect device function. The epitaxial growth of ideally shaped volumes depends on various factors, including fin height, fin shape, fin spacing (pitch), fin erosion, box gauging, and fin cleaning.